--- a/suite/common/utilityOverlay.js
+++ b/suite/common/utilityOverlay.js
@@ -1624,10 +1624,11 @@ function GetFileFromString(aString)
 {
   // If empty string just return null.
   if (!aString)
     return null;
 
   let commandLine = Components.classes["@mozilla.org/toolkit/command-line;1"]
                               .createInstance(Components.interfaces.nsICommandLine);
   let uri = commandLine.resolveURI(aString);
-  return uri instanceof Components.interfaces.nsIFileURL ? uri.file : null;
+  return uri instanceof Components.interfaces.nsIFileURL ?
+         uri.file.QueryInterface(Components.interfaces.nsILocalFile) : null;
 }